import com.sun.xml.internal.bind.v2.runtime.unmarshaller.XsiNilLoader;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Scanner;

public class sdf {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String str = scanner.nextLine();
        ArrayList array = new ArrayList<>();
        char[] str1 = str.toCharArray();
        for (int i = 0; i < str.length(); i++) {
            array.add(str1[i]);
        }
        if (str == null) {
            System.out.println(0);
        }else {
            int i = 0;
            int cur = 0;
            while(i<str.length()) {
                for (cur = 0; cur < i; cur++) {
                    if(str1[i] == str1[cur] || i-cur < 1) {
                        array.remove(str1[i]);
                        array.remove(str1[cur]);
                    }
                }
            }
            System.out.println(array);
        }
    }
}
